pgsql: Remove a few unused struct members.

Remove a few unused struct members.

Oversights in commits ab9e0e718a, f3049a603a, and 247ce06b88.

Author: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Discussion: https://postgr.es/m/aScUuBSawPWogUxs%40ip-10-97-1-34.eu-west-3.compute.internal

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/9446f918ace9c407805ba7d0a73e8370070b12f9

Modified Files
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src/backend/libpq/auth-scram.c            | 2 --
src/backend/storage/aio/method_worker.c   | 1 -
src/backend/utils/sort/sharedtuplestore.c | 1 -
3 files changed, 4 deletions(-)